Recent years have seen dramatic developments in the liquid crystal display using a liquid crystal panel, and the liquid crystal display is expected to be a substitute for cathode-ray-tube displays that are most widely used as display devices at present. Among these liquid crystal displays, the liquid crystal display of the active-matrix driving type, which is most commonly used, adopts an active element for each pixel so as to drive the pixel electrode by using this active element.
In the liquid crystal display of the active-matrix driving type, a liquid crystal panel is used in which a liquid crystal layer is sealed between a light-transmitting substrate (hereinafter, referred to as a substrate on the active-element side) having the active elements formed thereon and a light-transmitting substrate (hereinafter, referred to as an opposing substrate) that faces the substrate on the active-element side.
On the substrate on the active-element side, a plurality of scanning lines and a plurality of signal lines are formed in a matrix format so as to orthogonally intersect each other. At each of the intersections of this matrix, a pixel electrode is formed so as to apply a voltage to the liquid crystal, and a switching element is also formed thereat so as to selectively drive the pixel electrode. Active elements, such as TFTs (Thin Film Transistors), diodes and MIM (Metal Insulator Metal) elements, are adopted as the switching elements.
In the liquid crystal display of the active-matrix driving type, however, when there are wiring irregularities due to the scanning lines and signal lines formed on the substrate on the active-element side, display unevenness tend to occur in the vicinity of the wiring due to disclination of the liquid crystal molecules. As illustrated in FIG. 7, in order to avoid this problem, a conventional device provides a light-shielding film 32 (indicated by hatched regions in the Figure) having a matrix pattern that covers a wider area than signal lines 30 and scanning lines 31 formed on the substrate on the active element side. The display unevenness due to the disclination that occur in the vicinity of wiring can be covered with the light-shielding film 32.
The light-shielding film 32 also has the effect of preventing the active elements 33 from degradation in characteristics due to light. However, the light-shielding film 32 of this type, which is formed on the opposing substrate with a wide width, results in a reduction in the aperture rate of the liquid crystal display.
In order to solve the problem of the reduction of the aperture rate, a conventional arrangement is known in which a thick flattening film (having an insulating property) is formed on the active elements. In this arrangement, the irregularities of the wiring are alleviated by the flattening film on the active elements. Since the irregularities are alleviated, it is possible to prevent the occurrence of disclination in the liquid crystal molecules in the vicinity of the wiring. Further, it becomes possible to stack the pixel electrodes on the wiring with the flattening film interpolated in between. Thus, the aperture rate of the liquid crystal display can be improved.
Meanwhile, with respect to a method for controlling a gap between the substrate on the active-element side and the opposing substrate, a conventional arrangement is well known in which spacers are placed between the substrate on the active-element side and the opposing substrate. With respect to the method for placing the spacers, a wet spraying method and a dry spraying method are commonly used. In the wet spraying method, a volatile solution containing spacers dispersed therein is sprayed onto one of the substrates, and in the dry spraying method, spacers, as they are, are sprayed onto one of the substrates.
In the liquid crystal display having spacers that are placed as described above, however, the spacers are also sprayed onto the pixel electrodes. For this reason, liquid crystal does not exist in the spacer portions on the pixel electrodes, and light which is made incident on the spacer portions is always transmitted. Therefore, for example, in the case of a liquid crystal panel (normally white) which shows black display upon application of a driving voltage, the portions at which the spacers are located always show white display. These white-display portions result in a problem in which the contrast ratio of the conventional liquid crystal display decreases to a great degree.
Moreover, when the two substrates are joined to each other, since the above-mentioned spacers have a globular shape, the spacers come into point-contact with the respective substrates at the portions where they are located. This makes it difficult to obtain a gap with sufficient accuracy.
In order to solve the above-mentioned problem, for example, (1) Japanese Patent Publication No. 301040/1994 (Tokukaihei No. 6-301040) discloses a method in which: aperture sections are provided in a light-shielding film having a matrix pattern that covers signal electrodes, etc. except for pixel electrodes, photo-reactive resin and spacers are applied thereto in association with the aperture sections, and the spacers are secured by exposing them with light through the aperture sections from the back-surface side.
Further, (2) Japanese Patent Publication No. 181317/1996 (Tokukaihei No. 7-181317) discloses a method in which: a positive-working photosensitive resin is applied to intersecting portions of a light-shielding film having a matrix pattern that is placed on a color-filter substrate, and the photosensitive resin is patterned by exposure from the back-surface side by using the light-shielding film as a mask so that a gap-controlling layer is formed.
However, in the gap-controlling processes between the respective substrates of methods (1) and (2) as described above, the photosensitive resin (photo-reactive resin) has to be applied only to the portion except for the pixelelectrode portion or to the intersecting portions of the light-shielding film having a matrix pattern. For this reason, upon application of the photosensitive resin, a printing plate or a dispenser of a certain type is required. Moreover, in the methods (1) and (2), it becomes difficult to positively apply the photosensitive resin to the portion except for the electrode portion, as liquid crystal panels with higher precision are developed and as the wiring becomes finer.
Furthermore, method (1) requires an additional process for removing the unreacted portion of the photosensitive resin after the spacers have been secured. In addition, even in the above-mentioned methods (1) and (2), it is necessary to form a light-shielding film with a wide width in order to prevent defects in display due to the aforementioned disclination. Consequently, the problem of a reduction in the aperture rate is presented in the same manner.